1. Field of the Invention
The present invention relates to a battery apparatus and a battery state monitoring circuit each of which is capable of calculating the remaining power of secondary batteries such as the lithium ion secondary batteries.
2. Description of the Related Art
As for a conventional battery state monitoring circuit, there is known the apparatus the circuit diagram of which is shown in FIG. 2. For example, such a configuration is disclosed in Japanese Patent Application Laid-Open No. Hei 09-312172 entitled xe2x80x9cBATTERY PACK, BATTERY CHARGER, CHARGING SYSTEM AND CHARGING METHODxe2x80x9d. This official gazette disclosure relates to a battery apparatus called the Smart Battery System.
Each of the lithium ion secondary batteries for use in the Smart Battery System does not have a self-protection function as in the Ni-Cd battery and hence a circuit for over-charge protection is required therefor. For this reason, a battery voltage monitor circuit 4A for detecting the battery voltage and a switch device 12A for stopping charging of the battery from the outside are both provided therein.
A battery apparatus 22A receives, at a microcomputer 6A serving as information processing means, signals A3A and A4A which have been respectively output by a current monitor circuit 3A and a battery voltage monitor circuit 4A to monitor the battery voltages, the charging current and the discharging current of secondary batteries 7A, 8A, 9A and 10A. Then, the microcomputer 6A, using that information (the battery voltages, the charging current and the discharging current), calculates the remaining power of the secondary batteries 7A, 8A, 9A and 10A, and also controls the ON/OFF state of switching devices 12A and 13A used as current limiting means to control the charge and the discharge to and from the secondary batteries 7A, 8A, 9A and 10A.
The battery apparatus 22A configured in such a manner carries out the display of remaining power and stops charging of the secondary batteries 7A, 8A, 9A and 10A by the microcomputer 6A. The output voltages A3A and A4A are respectively input from a current monitor circuit 3A and a battery voltage monitor circuit 4A to the microcomputer 6A which can calculate the charging current, the discharging current and the battery voltages of the secondary batteries 7A, 8A, 9A and 10A on the basis of the voltages A3A and A4A thus input thereto to calculate the remaining power of the secondary batteries. In addition, since the microcomputer 6A carries out the ON/OFF control of the switching devices 12A and 13A on the basis of the state of the secondary batteries (in general, the over-charge, the over-discharge and the over-current states), the microcomputer 6A takes on itself the safety for the protection function (the over-charge protection, the over-discharge protection and the over-current protection) in the battery apparatus 22A.
The battery voltage monitor circuit 4A converts the respective voltages of the secondary batteries 7A, 8A, 9A and 10A into voltages which can be read by the microcomputer 6A to output the resultant voltages. For example, an example of a configuration of the conventional voltage monitor circuit 4A is shown in FIG. 6. The battery voltage monitor circuit 4A is a circuit including a change-over switch 33A, a battery voltage monitor amplifier 34A and the like. The change-over switch 33A selects the battery voltage of a respective one of the secondary batteries 7A, 8A, 9A and 10A one after the other, and the battery voltage monitor amplifier 34A converts the battery voltage thus selected into a voltage which is can be read by the microcomputer 6A to output as a voltage A4A to one signal line. Thus, which secondary battery is selected is determined on the basis of a control signal B4A which is controlled by the microcomputer 6A so that the voltages of the secondary batteries are successively output to the one signal line. In this connection, while as for the control signal B4A, only one line is illustrated in FIG. 6, it is also conceivable as the assembly of a plurality of signals. In addition, the diagram of the switches in the change-over switch circuit 33A shown in FIG. 6 is a schematic expression, and hence any switch configuration may be available for use as long as it can output the battery voltages one after the other.
However, since in the conventional battery voltage monitor circuit 4A as shown in FIG. 6, the battery voltages on the respective output lines of the secondary batteries 7A, 8A, 9A and 10A are successively output to the microcomputer 6A one after the other, the following performance is required.
First of all, a large number of switches are required for the change-over switch circuit 33A and hence a large number of signal patterns based on which of those switches are controlled are required. In addition, when the secondary batteries 7A, 8A, 9A and 10A are connected in series, the battery voltage monitor amplifier 34A, for the reason of outputting the respective voltage values, must be a differential amplifier, and needs to have a withstanding voltage which is equal to or higher than the total voltage of the secondary batteries 7A, 8A, 9A and 10A at the lowest, and also can output or cancel the offset voltage which has been generated depending on the input voltage level.
As described above, there arises the problem that since the conventional battery voltage monitor circuit has many performance requirements, the configuration of the circuit becomes complicated, and also since a high withstanding voltage processing is also required therefor, the circuit area is increased and hence the manufacturing cost of the circuit becomes high.
In the light of the foregoing, the present invention has been made in order to solve the above-mentioned problems associated with the prior art, and it is therefore an object of the present invention to configure the battery voltage monitor circuit with a simple circuit configuration and also to monitor the battery voltages with simple method to inexpensively provide a battery state monitoring circuit and a battery pack.
In order to attain the above-mentioned object, according to an aspect of the present invention, instead of the conventional battery voltage monitor circuit, there is provided a divided battery voltage monitor circuit which is capable of dividing the total voltage of a plurality of secondary batteries connected in series and the voltage of each of the connections into respective arbitrary voltage values to output the resultant voltage values. The divided battery voltage monitor circuit is realized with a simple circuit configuration and is miniaturized. In addition, there is also adopted a battery voltage monitoring method of calculating the battery voltages on the basis of the combination of the divided battery voltage values using a microcomputer as one constituent element of the battery state monitoring circuit.